The present invention relates to a method for controlling an EDM (Electroerosion or Electric Discharge Machine) via a control device provided with technical parameter sets connecting one of a group of input parameters with suitable output parameters.
In principle, an EDM machine can be controlled in a variety of ways. For example, at least theoretically, any conceivable type of electric pulse may be used. In addition, the manner in which the wire is controlled, such as the wire feed speed along the longitudinal direction of the wire, the wire tension, etc., may in principle be varied arbitrarily. The same applies to the other required control parameters, like flushing data.
Conversely, a preferred machining objective can in general be attained only by selecting a limited number out of all possible control parameters. The problem here is to select the ideal control parameters for a specific objective. This can be accomplished, but requires a great deal of experience and experimentation.
For this reason, modern EDM machines and their control devices, respectively, are provided with a number of available technical parameter sets including input parameter sets and output parameter sets, respectively. Input parameters, for example, may be machining objectives, workpiece and wire materials and the like. The output parameters comprise control parameters suitable for the respective input parameters. Consequently, a technical parameter set connects certain objectives with a suitable selection of control parameters.
DE 41 38 092 A1 discloses an example for a control method, e.g. for a sinker erosion machine, operating with technical parameter sets stored in memory. The input parameters, however, are purposely selected as "fuzzy", meaning in the form of parameter ranges, wherein the controller pre-selects from the parameter ranges specific input parameters which provide the best results with respect to machining time. For the pre-selected input parameters, certain output parameters are subsequently fetched from the stored technical parameter sets. It is presumed that respective technical parameter sets for all values from the input parameter ranges are available in the controller.
In reality, however, the number of technical parameter sets provided on the EDM machine is limited. An example for this limitation is the input parameter "workpiece height." A particularly thin workpiece may be machined with different electric pulses than a particularly thick workpiece. For establishing the respective technical parameter sets, it is not feasible to consider all conceivable workpiece heights. It is more convenient to restrict the height to a certain number of discrete values within a relevant range. It would be possible to have, for example, a technical parameter set for a workpiece height of 10 mm, another set for a height of 20 mm and another set for a height of 30 mm, each set for otherwise identical input parameters.
Frequently, however, the height of an actual workpiece to be machined lies between these discrete values, i.e. at about 25 mm. Similar arguments apply to the other input parameters.
In practical situations, for machining a workpiece, it is therefore usually desirable to select a technical parameter set which, although not ideal for the desired objective, is still adequate. In a machining operation with conventional technology, this is achieved in the following manner.
First, the control device indicates which values or possibilities, respectively, are present for a first input parameter in the available technical parameter sets. This may, for example, be the height of the workpiece to be machined. The user can now select one of these options. In the example, the user selects a workpiece height of 20 mm.
This selection, however, is not obvious if the actual workpiece height is 25 mm. It is, for example, conceivable that for an actually used EDM machine, values are preferably rounded up when the workpiece is thicker, and rounded down, when the workpiece is thinner. It is also conceivable that this rule is reversed for certain other input parameters. In addition, such a rule may depend on the material used for the wire and/or workpiece.
In a second step, the control device now displays all other available possibilities for a second input parameter. After a height of 20 mm was selected in the first step, the control device may now display all contour tolerances having associated with them technical parameter sets adapted for machining these tolerances at a workpiece height of 20 mm. Here again, the user has to make a selection.
The remaining input parameters are treated in the same manner. The control device then displays the remaining possibilities for each of these input parameters. After each option, the user makes a selection, whereby the number of possibilities for the next input parameter is reduced. Since technical parameter sets having exactly identical input parameters, but different output parameters are not permitted, exactly one technical parameter set is selected in this fashion.
If the procedure reflecting the present state of the art is represented in form of a diagram (FIG. 3), then the procedure corresponds to a hierarchical flow chart. In the example, there is a choice between three possibilities A, B and C at the starting point. Each of these possibilities A, B and C in turn represents a node where a selection can be made between the possibilities AI, AII and AIII, or between BI, BII and BIII. This procedure is repeated until an end point is reached.
The major disadvantage of this procedure is that the user has to make a decision at each of the nodes. As noted above, the user is required to have considerable technical know-how. In the end, the user has to know which of the available input parameters is best for providing the desired objectives. Consequently, the experience of a particular technical specialist is material for the efficiency of an EDM machine.